Thinkfan

I have a Lenovo Thinkpad T420s. It’s a nice little laptop. But the fan runs,
constantly, and annoys me. Thankfully, there’s a nice tool called
thinkfan!

On Debian Stretch with a Linux 4.x kernel, here’s how you can set it up to work
so that your fan only spins up at temperatures above normal levels, saving your
battery and keeping you from going insane due to fan noise:

Install thinkfan:

$ sudo apt install thinkfan

Enable the thinkfan service in systemd:

$ sudo systemctl enable thinkfan.service

Make sure the thinkpad_acpi kernel module loads with fan control enabled:

Create a thinkfan.conf file with sensible fan rates for sensible temperatures,
which looks like this, which will turn off the fan until the CPU temperature
reaches 48 degrees C and will turn the fan on full-blast above 63 degrees C: